This invention relates generally to a method for marking petroleum hydrocarbons with anthraquinone compounds for subsequent identification.
U.S. Pat. No. 4,755,012 discloses a ray absorption filter comprising a 1,4,5,8-tetra(arylamino)anthraquinone. This reference, however, does not suggest a method for marking petroleum hydrocarbons.
Phthalocyanine dyes having absorption maxima above 700 nm are known as petroleum markers, but these materials suffer from disadvantages, including difficulty of preparation and high cost. The problem addressed by this invention is to find an improved method for marking petroleum hydrocarbons with compounds having an absorption maximum above 700 nm.
The present invention is directed to a method for invisibly marking a liquid petroleum hydrocarbon. The method comprises adding to the liquid petroleum hydrocarbon at least one dye selected from the group consisting of 1,4,5,8-tetrasubstituted anthraquinones and anthraquinone dimers. The absorption maximum of the dye(s) is in the range from 710 nm to 850 nm.